Images from the Jewish Museum of Belgium show the gunman behind Saturday 's deadly attack approaching the building , opening fire , and walking away .

He used an AK-47 assault rifle to carry out the shooting , which killed at least three people , police said Sunday .

Photographs and video released by Belgian police show the man wearing a cap and blue shirt , carrying two bags over his shoulder . The images do not show his face clearly .

The shooter left on foot after the attack and headed toward a different part of downtown Brussels before he disappeared , according to police .

Authorities are hunting the suspect , believed to have acted alone , deputy public prosecutor Ine Van Wymersch said . Investigators hope the public will help to identify the suspect .

Two of those killed in Saturday 's attack are Israeli and the third is French , Van Wymersch said .

The Israelis were a couple in their 50s from Tel Aviv , Israel 's Foreign Ministry said .

French Foreign Minister Laurent Fabius said the French victim was a woman and offered his condolences Sunday to the families of all those killed , his ministry said .

A fourth person , a Belgian national who works at the museum , remains in critical condition , Van Wymersch said Monday . That contradicted museum spokeswoman Chouna Lomponda , who said Sunday that the fourth person had died .

Terrorism has not been ruled out , Van Wymersch said Monday . No arrests have been made , she said .

A person who was detained Saturday soon after the shooting is considered a witness and not a suspect , Van Wymersch added . That witness was not seen in surveillance video recorded during the attack , she said .

The circumstances of the shooting have raised suspicions that it may have been an anti-Semitic attack , but no motive has been determined . Van Wymersch said it was too early to determine whether the attack was an act of terrorism or motivated by anti-Semitism .

Could the killer attack again ?

A senior Belgian law enforcement official told CNN that Belgian police do not yet have any leads on the killer .

It 's been challenging to identify the killer because he was wearing a baseball cap .

The official told CNN that authorities have no information yet on the specific motivation or ideological background of the killer .

They do not know whether they are dealing with Islamist terrorism , some sort of neo-Nazi type of attack or another category altogether .

But there is concern that the killer could strike again , the official said , and that authorities could be dealing with a `` Mohammed Merah '' type of killer .

Merah , a French-Algerian Islamist radical who received terror training with al Qaeda-linked militants in Pakistan , shot and killed three French paratroopers in two attacks in March 2012 before killing three schoolchildren and their teacher at a Jewish school in Toulouse , France , during a 10-day shooting rampage which he filmed with a camera attached to his torso .

But the official stressed that no evidence has emerged in Saturday 's attack pointing to any link to Islamist terrorism .

The official told CNN that authorities can not say with certainty whether the Brussels gunman was carrying a video camera to film the attacks . Some investigators who viewed the surveillance footage believed this was the case and some did not . The quality of the surveillance footage was not good enough to make a conclusive determination .

The official said the killer shot the Israeli couple first in the museum entryway with one of his weapons . The couple had been consulting the wall display . He then pulled out a Kalashnikov assault rifle and shot the others inside the museum .

Surveillance cameras picked up the killer walking on two or three streets before he disappeared .

The official said the killer appeared to be skilled in using weapons and likely planned the attack meticulously .

The official stressed Belgian authorities are investigating all possible angles , including Islamist terrorism , neo-Nazi attack , and other categories . With regard to the threat from Islamist terrorism , he noted there has been longstanding concern over the 100 or so Belgian Islamist extremists who received training in the Afghanistan-Pakistan region over the years , and high current concern over several hundred who have more recently traveled to fight in Syria . The concern is they might be able to use skills acquired there to launch attacks back home .

Heightened security

Belgium 's Interior Ministry raised its terror alert level in the wake of the attack .

Belgian Interior Minister Joelle Milquet told a news conference Saturday that the security threat level was at its highest at locations frequented by the Jewish community across the country . This measure is precautionary , she added .

She met with the police , Belgian Jewish community leaders and the president of the European Jewish Congress , Moshe Kantor , on Sunday to discuss the security arrangements , an Interior Ministry statement said .

The Jewish community is determined to continue its activities in schools , synagogues and cultural centers , but under heightened security with a permanent police presence , the statement said .

Kantor is also to hold urgent talks with Belgian Prime Minister Elio Di Rupo , his group said in a statement .

Kantor described the attack as `` horrific but not surprising '' and urged action by European governments to tackle extremism and hate speech .

`` Attacks on Jewish targets in Europe do not exist in a vacuum , but are part and parcel of an overall climate of hate and incitement against Jewish communities , '' he said , according to the statement .

`` Anti-Semitism begins in the public domain , it gains international legitimacy and becomes normative even in our national parliaments but it always ends in killing Jews . ''

Pope Francis , who was in Israel on Sunday , told reporters that he had a `` heavy heart '' after the `` atrocious '' attack .

`` While reiterating my condemnation for this criminal act of anti-Semitic hatred , I entrust the victims of this crime to the God of mercy and invoke upon the wounded his gift of healing , '' the pope said in Tel Aviv before departing for Jerusalem .

Jewish men targeted in France

In neighboring France , two Jewish men were assaulted late Saturday as they were leaving a synagogue in Creteil , outside Paris , the French Interior Ministry said Sunday .

Two men were involved in the aggression against the two Jewish men , who are bruised , Interior Ministry spokesman Pierre-Henry Brandet said in an interview with CNN affiliate BFMTV .

Interior Minister Bernard Cazeneuve instructed police and other authorities to strengthen security at Jewish sites while looking for the perpetrators of Saturday 's incident , which he strongly condemned , according to the ministry .

In the wake of the attack in Brussels , Cazeneuve reaffirmed his determination to fight those who commit murderous acts and spread racism as well as well as anti-Semitism , the ministry said .

Anti-Semitism worldwide

A global survey released in May by the Anti-Defamation League reported on the levels of anti-Semitism found in 102 nations .

Belgium received a 27 % index score in the survey . The index score represents the percentage of adults in a country who answered `` probably true '' to a majority of the anti-Semitic stereotypes tested . Belgium has an adult population of about 8.7 million .

The ADL said one-fourth of adults worldwide are `` deeply infected with anti-Semitic attitudes , '' according to a CNN.com report on the survey .

France had the second highest index score in Europe , with 37 % , although that was well below Greece , with 67 % . Germany had a score of 27 % , Spain 29 % , Sweden 4 % and the United Kingdom 8 % . The United States was given an index score of 9 % .

More on rampage killings

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Senior Belgian law enforcement official says police have no leads

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The public prosecutor says the death toll stands at three , not four

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A museum spokeswoman said Sunday a fourth victim had died

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Two Jewish men were targeted in an attack outside synagogue , French Interior Ministry says